POSITION OF OPTIC ANLAGE IN AMBLYSTOMA 279 



lateral position so that it faced the median plane, and if the 

 lips or peripher}' of the optic cup failed to reach the ectoderm 

 the eye was without a lens. 



In none of the specimens, although many were old with the 

 central nervous tissue highly differentiated, was I able to detect 

 any material within the brain which might be considered as 

 representing the missing eye. 



Eye conditions such as these are doubtless due to the action 

 of some inhibitory influence which prevents the complete origin 

 and differentiation of eye material, or when it does arise allows 

 it to develop onlj^ in a weakened or defective manner. Since 

 monophthalmica asymmetrica occurs so persistently in the same 

 experiments with cyclopean individuals as Lewis, McClendon and 

 I have all found, it is not improbable that the cause is the same 

 in the two cases. 



The above considerations have been entirely from the stand- 

 point that the ophthalmic defects under discussion originate dur- 

 ing the medullary plate stage. The cause of cyclopia or the 

 tendency to produce such a defect might of course have its ori- 

 gin much earlier in development. It might, in fact, go back to 

 the germ cells themselves or finally it might possibly occur as 

 an hereditary variation. All experimental cyclopia, however, 

 furnishes evidence directly contrary to the latter possibilities. 

 This point I have considered in a previous paper and have 

 clearly demonstrated as have several other investigators that the 

 condition is not due to a germinal variation but may be induced 

 as the result of external stimuli applied during the early devel- 

 opment of the eggs. 



The cyclopean abnormality may be caused in Fundulus embryos 

 by subjecting the eggs to various chemical stimuli after they 

 have developed normally for as long as fifteen hours. A fif- 

 teen-hour Fundulus embryo has the germ ring beginning to form 

 and descend over the yolk sphere, the embryonic shield is scarcely 

 indicated but appears very soon afterwards. Embryos of later 

 stages subjected to the same treatment develop normally, or do 

 not show cyclopia, while stages younger than fifteen hours and 



